Mushroom Strudel - Chef Recipe by Antonio Carluccio

Name: Mushroom Strudel - Chef Recipe by Antonio Carluccio
Cuisine: European, German
Ingredients: 200 g (7oz) filo pastry; 60 g (2 1/4 oz) unsalted butter, melted; 1 medium egg, beaten, for wash; 1 medium onion, peeled and finely chopped; 40 g (1 1/2 oz) unsalted butter; 500 g (1lb 2oz) wild and cultivated mushrooms, cleaned weight; Freshly grated nutmeg; 1 Tbs dry sherry; 1 Tbs cornflour (cornstarch); Leaves from 1 sprig of fresh marjoram; 30 g (1 oz) Parmesan, freshly grated; Salt and freshly ground black pepper